1. Field of the Invention
The invention relates generally to the field of optics, and more particularly to optical add-drop multiplexers.
2. Description of Related Art
Reconfigurable optical add-drop multiplexers (ROADM) have become increasingly popular due to the emergence of dynamic networks. A service provider seeks the flexibility to add or drop any wavelength at any client site/node, which stimulates the development in the areas of tunable filters (TF), tunable laser sources (TLS) and reconfigurable blocking filters (RBF). Current solutions tend to be expensive while yielding mediocre performance. The optical industry remains years away from attaining an optimal design and manufacture solution that provides full reconfigurability at a low cost for next generation of optical networks.
In the interim, semi-reconfigurability solutions that are relatively inexpensive provide attractive alternatives when network carriers desire to contain costs. Two conventional designs of wavelength channel switching are commonly adopted. In a first approach, a transmissive structure employs a wavelength demultiplexer (demux), a wavelength multiplexer (mux), and an array of 2×2 fiber optical switches for directing a light beam to a desired path. However, the use of multiple discreet subcomponents renders this approach impractical since it causes a high-insertion loss as well as the high cost of using multiple discreet subcomponents.
In a second approach, the filtering and switching functions are integrated on a single device. An example of the integrated functions is a thin film based 2×2 add-drop fiber optical switch. One shortcoming of this device structure is that it does not produce a hitless feature, which is a desirable function for reconfigurability. The term “hitless” in this context means that there is no interruption or negligible interruption in the passage of express or non-drop channels when another channel is transitioning from drop to non-drop or non-drop or drop.
Accordingly, it is desirable to have a reconfigurable optical device that has a hitless switch capability.